Two Russian cargo planes carrying 80 tonnes of humanitarian aid have landed in Syria, Syrian state media say.

It comes amid reports that Russia is stepping up military support to the Syrian government.

The planes flew into an air base near the coastal city of Latakia, a stronghold of President Bashar al-Assad.

Russia has been a key ally of President Assad during Syria's bloody four-year civil war.

Analysts say that without the Kremlin's backing, President Assad may have fallen by now.

The planes flown in to Latakia on Saturday were carrying materials for setting up a tent camp for refugees, according to Russian Defence Ministry spokesman Maj Gen Igor Konashenkov.

He said the shipment included beds, mattresses, stoves, water cisterns and food.

Earlier this week, the US and Nato expressed concern that Russia was increasing its military presence in Syria.

The Kremlin has dismissed any military build-up, but Foreign Minister Sergei Lavrov said on Thursday that Russia would send more help to Syria if requested.

A handout picture released by the Syrian Arab News Agency (SANA) on September 12, 2015 shows members of the Syrian Red Crescent unloading a Russian plane carrying humanitarian aid on the tarmac of the Martyr Bassil al-Assad international airport in the government-controlled coastal city of Latakia. Two Russian planes carrying 80 tonnes of humanitarian aid landed in Syria, state media said, amid reports that Moscow is beefing up military support to its ally Damascus. AFP PHOTO / HO / SANA

"Russia is sending planes to Syria with both military equipment in accordance with current contracts and humanitarian aid," he said.

"Russia is not taking any additional steps."

Planes blocked

US officials have said Russia may be giving President Assad extra military support because he has suffered substantial territorial losses to rebels.

The Syrian government recently lost control of a key air base in the north-eastern province of Idlib.

Last Tuesday, Bulgaria refused to allow Russian aircraft to cross its air space amid fears that Russia was sending extra military support to Syria.

Russia later said it had been given permission to fly over Iranian territory en route to Syria.

On Wednesday, officials in Washington quoted by Reuters said Moscow had sent more aircraft and two tank landing ships to Russia's naval base in the Syrian coastal city of Tartus. They also said a small number of naval infantry forces had been deployed.

While Russia has backed the Syrian government and provided it with arms, the US wants to see President Assad removed.

The war between President Assad's regime and various rebel groups has so far killed at least 240,000 people and displaced millions.